Pneumatic control valve use for a period of time often appear this fault, the first valve stroke adjustment. Not up to the requirements, is usually the actuator or accessories leakage, actuator spring rigidity is not up to the requirements, push rod or stem bending, deformation, spool damage or spool, there is debris in the valve seat, medium flow direction is not correct, packing friction is too large and other original cause. Damaged spring, push rod, valve stem, valve core, valve seat should be replaced.
Check whether the air supply pressure meets the requirements; Check actuator accessories for leaks. Use soapy water to check. The flow direction of the medium is not correct, and it can be reversed. When the packing friction is too large, the packing gland can be loosened for lubrication and the valve stem can be rotated to reduce the resistance. Do not ignore the correct alignment of the valve positioner or electrical converter, but also check the position of the manual mechanism or travel stopper, and adjust it if necessary.
